I just want to reiterate this for u/BusyPhsyics8. I was in a serious accident when I was in my 20s that left me with a traumatic brain injury and chronic pain and weakness (luckily I'm mostly healed now, but it took a year or two). I looked able and healthy, but I had significant and unpredictable balance issues. I also had speech issues due to the brain injury, especially if someone put me on the spot and I was embarrassed or flustered. I used the handicapped stalls whenever possible even though I could get by without them, but the bars gave me a sense of safety in case I lost my balance.

If I'd been questioned by some random stranger about why I was using the handicapped stall, I would not have been able to answer, not that they'd be entitled to one anyway. I'm sure I would have stammered out a quick "no" and hurried out as I died of embarrassment. Luckily I never ran into any assholes like the OP.

You're not the disability police, OP, and your behavior is likely making it more difficult for people with invisible disabilities. Better keep working on that awareness of disability issues.